Protein binding of cholangiographic agents. With ultrafiltration techniques we are examining binding to human albumin, particularly with reference to competition for other tightly bound drugs. The data appear consistent with 2-3 separate binding sites, each demonstrating preferential affinities for specific drugs. Effect of meglumine diatrizoate on vasopressin induced changes in water permeability in the toad bladder. As as outgrowth of urine osmolality studies in the dog undergoing intravenous urography, the urographic contrast agents were studied for their effect on water permeability. The sodium salt was inactive, the meglumine salt was inhibitory. Inhibition was greatest with diatrizoate as an anion, less with smaller anions. Acute diuresis as a means of studying intra-renal drug distribution. As an outgrowth of the effect of intravenous urography on urea excretion, we are using acute diuresis with frequent short interval collection of urine as a semi-quantitative index of parenchymal drug distribution. The method is now being applied to phenacetin, paracetamol, and its conjugates. We plan to study the intra-renal distribution of diatrizoate, using insulin as a reference solute, during acute hydronephrosis and ischemic renal damage. Techniques will include tissue analyses and urinary excretory patterns.